JPS5952583A - Treatment of aqueous solution containing arsenic and iron using iron-oxidizing bacteria - Google Patents

Abstract

PURPOSE:To efficiently remove and recover arsenic, by effectively treating an aqueous soluion containing at least arsenic and iron using iron-oxidizing bacteria. CONSTITUTION:In the first step, an aqueous solution containing at least arsenic and ferrous ion above an amount equivalent to that of said arsenic is neutralized to a pH of 2.0-2.8 and then separated into a liquid and solid matter. The liquid is sent to the second step. In the second step, arsenic in the liquid sent from the first step is reacted with ferric ion returned from the third step undermentioned, to precipitate it as ferric arsenide. In the third step, the liquid after being dearsenided is introduced into an oxidizing tank, where ferrous ion in the liquid is oxidized into ferric ion by iron-oxidizing bacteria. The resulting liquid is returned to said second step. The iron-oxidizing bacteria in the third step are circulated together with the precipitate formed in the third step to the oxidizing tank for its reuse. A part of the liquid after being oxidized is returned to the second step, while the remainder is used for recovering the precipitate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for effectively treating an aqueous solution containing at least arsenic and iron, such as heavy metal-containing water produced in a hydrometallurgical smelting process, using iron-oxidizing bacteria.

In general, non-ferrous metal minerals contain toxic substances such as arsenic and cadmium in addition to the metals to be extracted, and these can cause various problems in the smelting process or be mixed into products and by-products, causing a decline in quality. It has become.

In particular, arsenic is volatilized during the process of melting raw material concentrate in a smelting furnace and concentrated in smoke. In recent years, as automatic smelting furnaces have been adopted as hexagonal smelting furnaces, SO
2 Because the concentration is high, it can be used as a raw material for sulfuric acid,
Since arsenic that does not settle in the flue is complemented in waste sulfuric acid in the sulfuric acid process, a method is known in which sodium hydrogen sulfide or the like is added to this to precipitate and remove it as AetSs. In addition, as another method, arsenic can be mixed with Fe such as ferric sulfate in a sulfuric acid solution.
How to coprecipitate with 3+ ions and JP-A Akihiroter 207j
There is also a method, as disclosed in Publication No. 2, in which As3+ is oxidized to As5+ using an oxidizing agent such as hydrogen peroxide, and then removed by coprecipitation with a hydroxide such as calcium hydroxide in an alkaline solution.

However, all of these methods require the use of a large amount of reagent to remove arsenic, and in cases where arsenic is particularly concentrated, operations such as two-step processing are required, which increases the amount of reagent required. This resulted in an increase in the amount of sediment and precipitate produced, leading to increased costs.

The present inventors focused on the fact that the sulfuric acid acidic solution produced in the hydrometallurgical process of wet smoke ash processing factories, etc. contains not only a high concentration of arsenic but also a large amount of Fe2+ ions. We have found an effective and low-cost method to oxidize this Fez+ to Fe3+ and then react and remove this Fe3+ with arsenic (Aθ3+).

Conventionally known methods for oxidizing Fe2+ to Fe3+ include adding oxidizing agents such as MnO2, KMnO+, C12, etc., and methods of oxidizing and precipitating by blowing oxygen under conditions of high temperature, high pressure, and high pH. Both require large amounts of chemicals and energy, and are expensive.

In addition, Fe2+ can be converted to Fe3+ using iron-oxidizing bacteria.
Japanese Patent Publication No. 17, 1987, proposed by the applicant as a substance that oxidizes to
7-31r, No. 11, etc., but these are mainly used to treat underground drainage, and the liquid produced in the smelting process, which has a high Fe2+ concentration and also contains a large amount of arsenic, is not suitable for use by the bacteria. It had been.

The present invention provides a method for efficiently removing and recovering arsenic from the smelting process liquid using iron-oxidizing bacteria. Explain in detail.

First, a neutralizing agent such as calcium carbonate is added to the liquid to be treated, such as the liquid produced in the smelting process, which contains at least arsenic (As'') and Fe2+ ions in an amount equal to or more than the equivalent of arsenic, and the pH is adjusted to 2.0 to 2.1. This is subjected to solid-liquid separation 94, and precipitates such as gypsum are separated and recovered, and the liquid is sent to a de-arsenization tank.

Fe3+ ions oxidized in the oxidation tank described later are returned to the arsenization tank, and a reaction with arsenic according to the following formula takes place.

As033-+ 2Fe"+ H2O→As0X-+.

2Fe +, 2H・・・・・・(1) ABO3
+Fe"+-+FeAe04 ・・a,,* ---
(2) This produces white FeAeO+ (iron arsenate)
Since this reaction occurs instantaneously, the reaction is completed after only a few minutes of stirring. In this case, F e”/A s
0% or more of arsenic can be separated by precipitation.

Table 7 shows the relationship between the pH of the neutralized liquid sent to the arsenization tank and the arsenic removal rate.As mentioned above, the pH during neutralization is between 2.0 and 2.0. It can be seen that the range of r is optimal. In addition, the Ae concentration before de-arsenization is ≠ 6 t/l.
used.

The iron arsenate produced in the arsenic removal tank has few impurities and is sufficiently concentrated in arsenic, so it can be used as a raw material for arsenite.
This arsenic grain is subjected to sedimentation separation, and a significant amount of unreacted Fe is recovered.
The dearsenization condensate containing 2+ ions is sent to an oxidation tank where it is oxidized to Fe3+ by iron-oxidizing bacteria. The oxidation tank contains iron oxidizing bacteria (Ferrobacillus).
Ferrooxldans + Th1obac11
ferrooxidance, etc.), and an acidic porous material such as diatoms is added as a carrier agent to maintain the bacterial cells. In addition, if necessary, nutrients such as N, P, etc., for example (NH
4) 2CO3, (NH,4)2804, K(,t
, K2H1)04t KH2PO4* Mg5Ot
- Add 7H20, Ca(NO3)2, etc. In addition, 8. S,, F, ct+ Zn, H
When bacteria-inhibiting elements such as g + Ag are included, it is desirable to remove them in advance through pretreatment. is removed by a settler etc. in the smelting process, F is 200 ppm, Ct is 10 (7 ppm
, Zn is 20? Since it has been confirmed in a beaker test that bacteria grow up to about 100 ml, a dilution method may be used if the concentration is higher than that.

Next, the liquid after the oxidation treatment is subjected to solid-liquid separation, and part or all of the precipitate containing diatomaceous earth carrying bacteria is repeatedly returned to the oxidation tank and reused for oxidation from Fe"+ to Fe3+, The required amount of the liquid oxidized to Fe3+ is returned to the dearsenization tank and used for the above-mentioned dearsenization reaction, and the remaining liquid is sent to the next step of iron neutralization.

Most of the liquid after solid-liquid separation after oxidation is iron-neutralized species, including CaO and C.
aCO5 = Ca salts such as Ca(OH)2 and alkaline agents such as sodium hydroxide, sodium carbonate, ammonium hydroxide, and magnesium hydroxide are added, and iron precipitates such as iron hydroxide and goethite are solidified. The liquid is separated and collected.

According to the method of the present invention, as described above, the large amount of Fez+ ions present in the liquid to be treated are oxidized by iron-oxidizing bacteria and used effectively to remove arsenic. It is very economical because there is no need to add special reagents for the oxidation of Fez+. Also,
By adding a small amount of a neutralizing agent to the remaining liquid after bacterial oxidation, the Fe content can also be recovered at a high yield.

Example/ The raw solution to be treated is decopper-removed condensate from the wet smoke ash treatment plant of smelter A, and its composition is shown in Table 2. Lead me to the tank
% Ca COs solution was added at II 00 nte 7 min and the pH was adjusted to 2. After adjusting and reacting, mix the gypsum precipitated with the thickener and the overflow water (flow rate/≠00
me/min). The composition of oats (-70-water) is shown in Table 3.

Table 3 Next, the overflow water is sent to the dearsenization tank and the ferric sulfate solution (flow rate 60θml 1 minute) from the bacterial oxidation tank is
The mixture was separated into iron arsenate precipitate and overflow water (flow rate: 2000ml/min) using a thickener. The compositions of this precipitate and the dearsenized oat flow water are shown in Table 1.

The overflow water after dearsenization contains iron oxidizing bacteria (valve concentration in the tank IJ-%), diatomaceous earth as a carrier agent (concentration in the tank!rOrny/l), and ammonium phosphate as a nutrient (concentration in the tank J OtnI- /l) is added and led to an oxidation tank for oxidation treatment, and after solid-liquid separation of the oxidized condensate liquid, a part of the liquid is returned to the de-arsenization tank.
The precipitate was returned to the oxidation tank.

As a result, nearly 9% of the arsenic in the highly concentrated arsenic-containing liquid was removed, as can be seen from Table 1.

The stock solution to be treated in Example 1 is a decopper-removed condensate from the same wet smoke ash treatment plant as in Example 1, and its composition is as shown in Table 5.

Add %CaCO3 to this stock solution (flow rate 2200me 1 minute).
Add solution (≠00ml/min) to adjust the pH! The neutralized condensate, which was automatically adjusted to , 2, is mixed with gypsum and overflow water (
The overflow water was sent to a de-arsenization tank and reacted with Fe3+ ions from the oxidation tank. The composition of the overflow water after neutralization is shown in Table 6.

Further, Table 7 shows the precipitation of iron arsenate from the arsenic removal tank and the composition of the arsenic removal liquid.

Hereinafter, as in Example 1, this dearsenized liquid was introduced into an oxidation tank in which ammonium phosphate was sprinkled over a diatom surface containing iron oxidizing grouperia, and oxidation treatment was carried out. The oxidized condensate was separated into precipitate and overflow water using a thickener, a portion of the precipitate was returned to the oxidation tank, and excess precipitate i was extracted from the system. A portion of the overflow water (1) was returned to the arsenic removal tank and used for reaction with arsenic, and the rest was sent to iron neutralization. The composition of the overflow water after bacterial oxidation is shown in Table g.

In the iron-neutralized species, slaked lime solution was added, and after the reaction, the mixture was separated into precipitate and overflow water. The precipitate is an iron precipitate mainly composed of iron hydroxide, and the composition of the precipitate and overflow water is shown in Table 1.

It shows a removal rate of about 1%, and a removal rate of 2% for Fe, making it possible to remove arsenic more efficiently and economically than conventional methods.

[Brief explanation of the drawing]

The figure is a flow sheet of an embodiment of the method of the present invention. Patent Applicant Dowa Mining Co., Ltd. Procedural Amendment (Voluntary) 1937 $4.18 Patent Office Commissioner Kazuo Wakasugi 1, Indication of the Case Patent Application No. 77-778-77 2, Name of the Invention: Iron-Oxidizing Bacteria Process for treating aqueous solutions containing arsenic and iron using a / line "For example, hydrometallurgical smelting process"
Correct the statement to ``For example, smelting 2nd degree''. (2) Specification tube ≠ page λth line l-' (A e”) j
Delete. (3) In page 7, line O of the specification, "Oxygen is blown under the conditions of 11" in "High ■) Oxygen is blown under the conditions of 11" is corrected to ``Blow air under the conditions of U-high p I-1 -J''. (4) Delete I-(As”)J on page j/line of specification tube. (5) 1 = acidic porous material J on page 7/~2 lines of specification tube
Correct the statement to read "acid-resistant porous material." (6) 11・゛ is 200 on page 7, line 70 to // of the specification.
p 'pm, CA is / 00 p p m J, 1F is / 00 Dpm, C1 is 10θOp p m
Correct with J. (7) In Table 12 on page 7 of the specification, it says "As3+J and 1A day" and in Table 3 on the same page, it says "I-A33F".
-AeJ and correct respectively. Below 1

Claims (4)

[Claims] (1) Water mW containing at least arsenic and ferrous ions
A first step of neutralizing the liquid to pH 2.0 to ノ, male, and reacting arsenic in the solution after the first step reaction with ferric ions obtained from the third step described later to remove iron arsenate and precipitate. In the second step of
Containing arsenic and iron using iron-oxidizing bacteria, the method comprises a third step in which iron ions are oxidized to ferric ions by ferric acid bacteria, and the oxidized solution is returned to the second step. A method for treating aqueous solutions. (2) The liquid to be treated in the first step contains ferrous ions in an amount equal to or more than an arsenic equivalent.
Treatment method described in section. (3) The iron-oxidizing bacteria in the third step are recycled to the oxidation tank together with the precipitate produced in the third step, and a part of the oxidized liquid is returned to the second step to collect the remainder. The treatment method according to claim 1 or 2, wherein the liquid is used for recovering iron precipitates. (4) Diatomaceous earth is added as a carrier agent for iron oxidizing bacteria, 7teria, and nutrients for the bacteria are added to the oxidation tank in the third step. Treatment method described in section.